Gut Microbiome and Thyroid Dysfunction

We’re in the midst of a hypothyroid epidemic—with almost 30 million people struggling with a thyroid condition and many more undiagnosed.

Women are much more likely to struggle with a thyroid problem than men (one out of eight are affected in their lifetime, and the odds become more likely as you get older). (1) In fact, thyroid cancer rates are also on the rise, while most other cancers have seen a steady decline over the past decade.(2) It begs the questions: why is the thyroid becoming susceptible to injury and harm? Like most chronic and degenerative conditions, there are many factors at play, but a critical one is your microbiome.

As a newborn, the bacteria that you’re exposed to sets the tone for shaping your microbiome (which includes the trillions of “good” and “bad” gut bacteria that live in your digestive tract). How important is the microbiome to your health? Consider early research, which suggests 9 out of every 10 cells on your body is the result of bacteria (and more recent studies suggest a 2:1 or 1:1 ratio). In fact, the overwhelming majority of the DNA on your body comes from the bacteria in your gut and on your body. (3) It’s likely that the interaction between the two influence your health and vitality.

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Your thyroid gland is effectively a bellwether for overall health, signaling a problem in another part of the body. It’s like the lights on the dashboard of your car; your thyroid alerts you to a problem elsewhere in the body. Therefore, when your microbiome gets out of balance, your thyroid gland will be negatively affected, which results in poor cognitive function, low mood, sluggish metabolism, and poor energy levels.

What common factors can cause an imbalance in gut bacteria? The following is a quick list of common aggravators:

Western diet (i.e., lots of processed carbs)

Excessive sugar intake

Being overweight

Overuse of antibiotics

High stress levels

Overuse of drugs that lower stomach acid

Birth control pills

Gluten consumption

Lack of exercise

Excessive high-intensity exercise

Unfortunately, conventional medicine only treats the symptoms. It doesn’t address the fundamental question of “why” your microbiome (and thyroid) are unbalanced in the first place.

Your diet plays a fundamental role in shaping your microbiome, but the bacteria in your gut plays a massive role in supporting optimal thyroid health. Let’s take a closer look at what happens when your microbiome gets out of balance.

Gut Bacteria and Blood Sugars

Recently, researchers made a major discovery about the impact your microbiome has on your blood-sugar response to meals. The glycemic index (GI) is a measure of how quickly the sugars from the food you eat get into your bloodstream.

In general, the more slowly and steadily your blood sugar levels rise, the better off you’ll be (in terms of health and body composition). Conversely, high-GI foods rapidly increase blood sugars, leading to the increased likelihood that you’ll store more of the “excess energy” as body fat. New research also leads to poor cardiovascular and cognitive health in the long term.

A recent study decided to try out the GI-index hypothesis by testing over 800 different people (both fit and overweight) with the same exact foods. In theory, the GI-index of a food should be very similar for all individuals. However, in practice, researchers found markedly different blood sugar responses to exactly the same foods.(4)

Overweight subjects eating low-GI snacks exhibited very large blood sugar spikes. And thus, the authors concluded that gut bacteria was exerting a significant impact on blood-sugar response from person to person.

In short, your gut bacteria plays a major role in your blood-sugar response to food (regardless of whether or not it’s a “healthy” choice). Big blood-sugar swings lead to energy crashes, and a subsequent overreliance on caffeine and sugar for energy. Blood sugar and insulin dysfunction is a major, underlying cause of thyroid dysfunction, and restoring a healthy balance of gut bacteria is crucial for stabilizing blood sugars.

Microbiome and Chronic Inflammation

If your microbiome is out of balance, you’ll likely struggle with consistent bouts of gas, bloating, constipation (or loose stools), and digestive discomfort. An imbalance of “good” to “bad” gut bacteria (known as dysbiosis in medical terms) can wreak havoc on thyroid function, because it can trigger a systemic inflammatory response in your immune system. Your gut is home to over 80% of your immune system, and inflammation is its first response to an insult or damage.

Inflammation is your body’s first response to damage, and can throw off your thyroid functioning.

Chronic inflammation throws off your thyroid function in a couple of ways. First, inflammation ignites a fire in your brain (upstream of your thyroid gland), dampening the message from your brain to your thyroid to produce thyroid hormone.(5) This change results in low TSH output from the brain, and thus low T4 output by your thyroid. The less thyroid hormone your body makes, the less energy every single cell in your body receives. (No wonder you’re tired).

Next, inflammation impairs hormone conversion downstream of your thyroid at the tissue level.(6) The fires of low-grade inflammation wear out the receptors at the tissue level, much like fraying the charger connector on your iPhone. Once it no longer fits, you can’t recharge your phone. Similarly, your body can’t recharge its cell and convert T4 into the active T3 hormone.

Microbiome and Thyroid Hormone Conversion

One of the most overlooked aspects of thyroid health is the conversion of thyroid hormone. Your T4 hormone (i.e., thyroxine) is made by your thyroid gland, and it must be converted to the “active” T3 (i.e., triiodothyronine) thyroid hormone to exert its positive effects in your body. If you can’t effectively convert T4 into T3, you won’t reap the benefits of healthy thyroid function (such as a clearer mind, better mood, quicker metabolism, healthy bowel function, and healthy skin).

A healthier thyroid means a clearer mind, a better mood, and faster metabolism!

Once again, dysbiosis and an imbalanced microbiome is a major roadblock to thyroid hormone conversion. In fact, 20% of your T4 thyroid hormone is converted to the active T3 form in the gut. Therefore, if you struggle with regular gas, bloating, constipation, or consistent discomfort, then chances are you’ll have poor conversion.(7) In short, if your digestive system isn’t running smoothly, your thyroid won’t likely be either.

How to Build a Healthy Microbiome

If you look at modern hunter-gatherer tribes (such as the Hadza in southern Africa) that mimic our Paleo ancestors, you’ll see stark differences in gut bacteria, compared to Western men and women. The Hadza gut microbiomes have much greater bacterial diversity and richness, compared to those in industrialized countries.(8)

A recent study compared the microbiomes of Western children to those living in rural areas of north Africa, where exposure to sugar and a Western diets is nonexistent. Researchers found incredible contrasts in bacterial diversity between Western and rural African children.

The Western children’s microbiome was predominantly made up of a family of bacteria called firmicutes (fer-MI-cue-tees), whereas the rural African children’s microbiome was made up of primarily the bacteroidetes family (and little firmicutes), and robust diversity of “good” gut bacteria.(9) Excessive firmicutes is problematic because it’s capable of synthesizing sugars at a rate of 100x more than other bacteria. When levels are high (typically due to consuming too much sugar or processed carbohydrates), you’re more likely to develop dysbiosis (and possibly more likely to struggle with thyroid dysfunction).

Your diet is the fundamental player in establishing your microbiome. When you’re struggling with dysbiosis, mimicking our hunter-gatherer ancestors is a great place to start. Here’s a short-list of nutritional interventions to start the process of rebuilding a healthy microbiome:

1. Eliminate Added Sugars and Processed Carbs

The consumption of added sugars dramatically changes the balance of “good” to “bad” bacteria in the gut. And as discussed above, reducing sugars in the diet is an effective strategy for supporting beneficial bacteroides levels and limiting firmicutes buildup in the gut. (9)

2. Eliminate Caffeine

When you’re struggling with a thyroid dysfunction, you’ll progress much more quickly if you abstain from coffee and caffeine. (The good news is: it’s likely not forever!).

3. Eliminate Alcohol

Alcohol contains sugar and yeast, which can aggravate a dysbiotic gut. Like caffeine, your best is to completely omit alcohol for 4-8 weeks, then reassess.

4. Limit Fruit

Morning breakfast smoothies are great, but the “carb count” can quickly ramp up when juice or fruit is added into the mix. Remove all added juice (even cold-pressed juices), and stick with water. As for fruit, replace higher-carb fruits (such as bananas and apples) with lower-carb, higher-fiber options (such as raspberries, blackberries, and strawberries).

5. Add More “Slow” Carbs

Reducing carbohydrate intake is helpful for reducing the levels of “bad” bacteria in the gut. However, not all carbs are created equal. Adding more “slow carbs” to your regime (which contain significant amounts of fiber) is a great way to support a healthy microbiome. For example, cooked and/or cooled plantains and sweet potatoes are great sources of resistant starches, which support healthy gut bacteria.

6. Add Fermented Foods (in small amounts)

Fermented foods can help restore a healthy gut, but they can also aggravate things. The key is to start slow. For instance, try adding a pinch of sauerkraut to dishes once a day. If you feel good, include more of these foods in your diet. If fermented foods aggravate your gut, you may have dysbiosis rooted in yeast overgrowth. (Talk to your local naturopath, doctor, or functional medicine practitioner.)

7. Add a Soil-based Probiotic Daily

Soil-based probiotics are sourced from the earth, which has suffered serious losses of natural biodiversity (due to industrial farming techniques). Since our food grows in dirt with less “good” bacteria, this change can shift your microbiome in the wrong direction.

Add one capsule daily of soil-based probiotics. And if you really struggle with gut health, you’ll likely benefit from adding a regular probiotic high in lactabacillus rhamnosus and bifidobacterium longum (to restore healthy gut balance).

The Bottom Line

It may seem daunting to make so many changes, but fear not. A few weeks or months is typically sufficient to reshuffle the balance of healthy gut bacteria and start reversing thyroid dysfunction. Get started with these simple tips. Your brain, body and thyroid will thank you for it.

Dr. Marc Bubbs

Dr. Marc Bubbs, ND is a Naturopathic Doctor, Strength Coach, Author, Speaker, and Blogger practicing in Toronto, Canada. He believes that diet, exercise, and lifestyle factors have the most profound impact on your overall health and performance. Marc is the author of The Paleo Project – A 21st Guide to Looking Leaner, Getting Stronger, & Living Longer and currently serves as the Sports Nutrition Lead for Canadian Men’s Olympic Basketball Team.